The present invention relates to a new and improved process of smelting sulphidic copper ore concentrates in which the ore concentrates are first partially roasted and the smelting is completed after the separation of the hot roasting gases from the ore.
In the classic refinement of copper ore, the ore is mined and formed into an ore slurry in a mechanism such as a ball mill, and the slurry is received by a flotation cell with chemicals bringing the copper minerals to the top to be removed and dried. The concentrate is then treated in a reverberatory furnace which shoots flames above the copper ore concentrate, and as impurities rise to the top and form a slag, the slag is drained off leaving a copper matte. The copper matte is passed to a converter with the remaining blister copper being 97% or more pure. The blister copper is usually further treated, such as, for example, by being cast into anodes and electrolytically refined.
The present invention relates to an improved smelting process for removing impurities from sulphidic copper ore concentrate. The copper concentrate is generally received, as above stated, from the flotation process, and in the flotation process, the concentrate that is received is high in sulphur content. Upon the melting of the sulphidic copper ore, it is necessary to remove a part of the sulphur before smelting the copper to obtain the copper matte or metal. This is done by a roasting process in vertical furnaces or in rotary kilns, and the roasting may be accomplished in a whirling layer roasting furnace for obtaining a more accurate maintenance of optimum roasting temperature.
In the roasting process, the gas which is released is separated by means of cyclone separators and is also subjected to further cleansing or purifying, such as in electrofilters, and is conveyed to a sulphuric acid installation. By means of the partial roasting, the sulphur content of the copper ore concentrate is reduced so that the exhaust gases attained in the reverberatory furnace contain a SO.sub.2 content of a maximum of 1% to 2%. This sulphur dioxide content is too low to be economically feasible to separate it from the exhaust gases. On the other hand, the sulphuric dioxide content is sufficiently high so that it exceeds the practical and the legally prescribed limits or conditions of discharge into the atmosphere and, therefore, the reverberatory furnace cannot be operated practically with sulphur dioxide discharges of these values.
For these reasons, contemporary methods have used a so called suspended melting arrangement in which the roasting and melting process is carried out simultaneously in one furnace unit, and the exhaust gases of a sulphur dioxide content sufficiently high for the economical production of sulphuric acid. It is a characteristic of this method that the selective oxidation as well as the melting step of the ore concentrate take place in suspension in a vertical shaft. In the transition of heat in the vertical column or shaft for sufficient melting of the ore, radiation and convection and conduction are used, and further the exothermic heat which is released upon the oxidation of the iron and sulphur in the concentrates is also utilized. This process, however, will result in a product substantially richer in copper than with the reverberatory process, and a copper matte product of over 60% of copper will result. However, counterbalancing the advantage of a substantially autogenous process of simultaneously roasting and melting the ore concentrate and the advantage of an exhaust gas rich in sulphur dioxide, there is a disadvantage of the copper-rich slag which results as a by-product. These slags require additional refining so that it has become necessary to provide an additional electro-furnace for the processing of the slag.
It is accordingly an object of the present invention to improve heretofore used methods and apparatuses for the refining of sulphidic copper ore concentrates so that the by-product of nonutilizable gases low in sulphur dioxide is prevented, and the entire smelting process becomes more economical and better adapted to the environment.
In accordance with the principles of the invention, the hot roasting gases are enriched with oxygen, and these enriched gases are utilized for supporting combustion in the smelting furnace instead of using secondary air.
The heat content of the smelting gas is made use of for the completion of the smelting process which leads to the appreciable reduction of fuel consumption. The incorporation of appreciable quantities of specific heat from the smelting or roasting gas results in an indirect technical utilization of the oxidation heat from the roasting process. Furthermore, the heat transition in the gas of the smelting operation in the reverberatory furnace is obtained for the greatest part through radiation. Support of combustion for heating by the roasting gas in the reverberatory furnace and with the use of oxygen, a very hot flame results which has an appreciably stronger capability of radiation heat transfer than a flame produced by means of secondary air with a supporting flow of nitrogen contained therein. Further, this results in an advantage in an increase in the smelting output of the furnace, thereby increasing the overall economy of the operation and capacity of a given smelting furnace.
In accordance with the method of the invention, utilizing the smelting gas enriched with oxygen instead of secondary air, the sum or the quantities of the exhaust gas from the roasting and smelting process is appreciably reduced because the nitrogen utilized in methods heretofore employed is eliminated. The recuperation of the heat content of the gas from the roasting and smelting material leads to a decrease in use of fuel, and this, therefore, reduces the overall quantity of gas employed for smelting a given quantity of material. Lastly, the roasting and reverberatory furnace represents one entity so that lower operation costs results. Also, because of the final exhaust gas being rich in sulphur dioxide, useful sulphuric acid recovery can be attained.
The method according to the invention utilizes a roasting smelting furnace with a cyclone separator attached on the exhaust side and a reverberatory furnace connected in series in which the hot roasted material separated off by the cyclone is melted to a copper matte, and the cyclone exhaust conduit of the cyclone is connected with the combustion air feed conduit of the burner. The roasting furnace is suitably arranged in such a manner above the reverberatory furnace such that the roasting material from the roasting chamber and from the cyclone feeds by gravity into the reverberatory furnace.
While the roasting material previously was collected into intermediary containers, it is now possible in accordance with the present method to introduce the roasting material from the cyclone separator through a charging valve directly and continuously into the furnace. The continuous charge of roasting material has reduced the quantity of exhaust gas in view of the improved economy of the process. A decrease in speed of the gas leads to a lowering of the dust loss upon charging of the roasting material.
It is accordingly an overall object of the invention to provide an improved intermediate process for the smelting and refining of copper which effects substantial economies and provides improvements over arrangements heretofore available.
Other objects, advantages and features, as well as equivalent methods and structures which are intended to be covered herein, will become more apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiment in the specification, claims and drawings, in which: